Implement support for touch-action: pan-x/pan-y in chromium

content/common/input/touch_action.h

Index: content/common/input/touch_action.h
diff --git a/content/common/input/touch_action.h b/content/common/input/touch_action.h
index 95cee2595b2256da34b34af3a0b14b3f9978023e..6bd2ddbc8bd7f6e67837e498f59598bd6a8a50ac 100644
--- a/content/common/input/touch_action.h
+++ b/content/common/input/touch_action.h
@@ -11,13 +11,19 @@ namespace content {
 // (panning and zooming) are currently permitted via touch input.
 // See http://www.w3.org/TR/pointerevents/#the-touch-action-css-property.
 enum TouchAction {
+  // All actions are pemitted (the default).
+  TOUCH_ACTION_AUTO = 0,

[jdduke (slow), 2013/12/19 16:17:16]

In the future, having TOUCH_ACTION_AUTO be the union of the flags, with
TOUCH_ACTION_NONE == 0 might be useful, but there are few enough combinations
here it's not a big deal.

[Rick Byers, 2013/12/19 16:35:09]

We can't actually - the semantics are different.  Auto permits pinching for
example where TOUCH_ACTION_PAN_X | TOUCH_ACTION_PAN_Y doesn't.  So there's
always going to be some 'flag' that can't be combined with any others.

We debated a little on the blink side (and changed it once) about whether AUTO
or NONE should have the value 0 - the benefit to AUTO being 0 is that AUTO is
the default (same as unspecified) and so will be the 99% common case on the web
for awhile.  But as long as we have this impure-flags semantics, then it's never
going to be simple.  Also I now COMPILE_ASSERT that the 3 different definitions
of this enum match their values exactly.

See http://msdn.microsoft.com/en-us/library/Windows/Apps/hh767313.aspx for
details on the larger set of semantics IE has here.

+
   // No scrolling or zooming allowed.
-  TOUCH_ACTION_NONE,
+  TOUCH_ACTION_NONE = 1 << 0,
 
-  // All actions are pemitted (the default).
-  TOUCH_ACTION_AUTO,
+  TOUCH_ACTION_PAN_X = 1 << 1,
+
+  TOUCH_ACTION_PAN_Y = 1 << 2,
+
+  TOUCH_ACTION_PAN_X_Y = TOUCH_ACTION_PAN_X | TOUCH_ACTION_PAN_Y,
 
-  TOUCH_ACTION_MAX = TOUCH_ACTION_AUTO
+  TOUCH_ACTION_MAX = (1 << 3) - 1
 };
 
 }  // namespace content